Issue: June 23, 1997

Euonymus scale insect problem

Question:

I have had a fungus problem on my euonymus, but that has
been quite well controlled. The real problem now is the aphids.
I am enclosing a leaf with the aphids and their trash. I first
noticed them two years ago. I sprayed them with several
insecticides in rotation and even put hot soapy suds on them. The
insects are thriving, getting worse, and spreading.

Unless you can help me, I fear I might need to dig the hedge
out.

Answer:

The insects on the leaf sample are not aphids - they are
Euonymus Scale, an insect which is specific to euonymus. In New
Mexico, many of our euonymus hedges are infested with this
difficult to control pest. Many people have indeed chosen to
remove the hedge rather than continue to fight the scale.

Scale insects are particularly difficult to manage because
as the insects mature, they settle down to feed on the plant at a
single point. They then build a waxy covering over themselves.
This covering protects them from the environment and our
insecticides. Before they settle down, the juvenile insects are
called "crawlers". In the crawler stage they are much more
susceptible to application of insecticides.

The insecticides you have been using are not all effective
against euonymus scale. There are several insecticides labeled
for euonymus scale control; these are the ones you should use.
They are all most effective when used against the crawler stage
of the scale insect. In New Mexico there may be several
generations of these insects each year, so you may have several
opportunities to apply these products. When you do use
insecticides, it is important to follow the label directions to
maximize the effectiveness of the product and to protect yourself
and your environment.

To determine if the crawler stage of the scale is present
and treatment appropriate, hold a sheet of dark-colored
construction paper or cardboard under a branch of your euonymus
and sharply strike the branch. Look for small insects crawling
around on the paper. With a magnifier you can confirm that these
are scale insects if you are familiar with their appearance. The
presence of crawlers indicates that treatment is appropriate.

Sanitation, removing fallen infested leaves and pruning
severely infested branches, is another important aspect to
treatment. The white material on your euonymus leaves are the
adult male scale insects. The adult females are brown and more
commonly found on the twigs. Removing them by pruning and raking
reduces the opportunity for reinfestation following spray
treatments.